I truly don't get it.
"hiding and being suspicious" and "looking suspicious" are synonymous to me.
Well they are not to me. At school, Trayvon was somewhere he was not supposed to be and he was concealing himself from view. That's objective behavior on which to base suspicions. Zimmerman's own account on the non-emergency line gives no objective reason to be suspicious of Trayvon. I find nothing suspicious in walking back to his father's fiance's townhouse and looking around and he gave no reason for saying that he's on drugs or something and later emphasizing that by saying "yes, he's messed up."